The present invention relates to a circuit for preventing crosstalk between adjacent circuits such as acoustic circuits.
Heretofore, various circuits have been proposed for preventing reduction of sound quality caused by crosstalk.
One of the methods for preventing crosstalk is reduction of the length of a signal line. A long signal line causes stray capacitance to increase, which may generate crosstalk, causing distortion of an audio signal.
FIG. 5 shows a conventional audio amplifier. The audio amplifier has operational amplifier OP1 for the left stereo channel and operational amplifier (hereinafter called opamp) OP2 for the right stereo channel. The non-inverting terminal of opamp OP1 is connected to input terminal Li of the left stereo channel (hereinafter called L-channel) through variable resistor VR1 and source changeover switch SW1. The inverting terminal of opamp OP2 is connected to gain setting resistors Ra1 and Rb1 and the other end of Rb1 is connected to an intermediate point between voltage dividing resistors R1 and R2.
The non-inverting terminal of opamp OP2 is connected to input terminal Ri of the right stereo channel (hereinafter called R-channel) through a variable resistor VR2 and a source changeover switch SW2. The inverting terminal of the opamp OP2 is connected to a gain setting resistors Ra2 and Rb2 and the other end of Rb2 is connected to a voltage divider comprising the resistors R1 and R2.
Audio signals from the input terminal Li and Ri are amplified by opamps OP1 and OP2 and output from output terminals Lo and Ro.
In such an audio amplifier, stray capacities generate, for example stray capacitance C1 and C2 between the output terminal Ro and a point a and between the output terminal Lo and a point b. Consequently, crosstalk is generated between the output terminal Lo and Ro. The crosstalk generated is remarkably when a high frequency signal is included in the audio signal. The crosstalk reduces the sound quality of the output sound.